This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from my application entitled METHOD AND SYSTEM FOR TEACHING WELDING ROBOT filed with the Korean Industrial Property Office on Feb. 11, 2000 and there duly assigned Serial No. 2000-6488.
1. Field of the Invention
The present invention relates in general to methods for correcting teaching points for welding robots and welding robot systems employing the same, and more particularly, to a method for correcting teaching points for a welding robot, by means of a touching sensor, and a welding robot system employing the same.
2. Description of Related Art
Recently, an arc welding has been widely used for industrial applications to weld a variety of materials such as steel sheets, etc. The arc welding generates an arc between a welding torch and workpieces or base metals to be welded and melts a welding wire and the workpieces with an arc energy, to weld the workpieces.
To perform an arc welding, a supply voltage, a distance between a welding torch and a workpiece, a supply speed of a welding wire, a weaving speed of the welding torch, and an initial welding point and a terminating welding point on a welding path, etc. are preprogrammed into a welding robot system depending upon a kind of the workpiece and a quality of welding, etc.
Especially, to perform a high quality of welding, a position of the workpiece should be identified exactly prior to welding. However, errors may be created from positioning devices such as a positioner or a welding jig to fix the workpiece, or from the workpiece itself. Because of these errors, it is not easy for the welding robot to be operated exactly on a desired welding point.
Various tracking techniques have been developed in order to track an exact position of the workpiece. The tracking techniques include an arc sensor tracking, a laser sensor tracking, a touch sensor tracking, etc. The arc sensor tracking uses an arc sensor to correct a displacement of the workpiece in real time when performing a weaving operation against the workpiece to be welded. The laser sensor tracking processes image data for the workpiece obtained by means of a laser vision camera, in order to correct a displacement of the workpiece in real time. The touch sensor tracking is to detect an initial welding point under the state that the workpiece is displaced. The displacement of the workpiece can be corrected in real time by using any of the above-mentioned tracking techniques as necessary.
The arc sensor tracking does not separately need any additional equipment; however, it needs a high-priced software option. The laser sensor tracking is the most typical tracking method, which has a high-performance but requires high-cost additional equipment such as a special laser sensor, etc. In addition, in the laser sensor tracking, a variety of sensors and devices should be attached closely to the welding torch installed at the end of a welding robot""s hand, thereby resulting in narrowing a space for welding operation. A main controller which is generally realized as a computer system performs operations of monitoring and sampling a variety of data; and therefore, as the additional equipment increases in number, the likelihood of causing an error in the course of operating the system increases accordingly in a multi-control process during the welding operation. Furthermore, the maintenance and repair of the additional equipment are highly complicated.
Korean Patent Laid-Open No. 98-27370 to Hwang and Hong, titled xe2x80x9cA method for controlling a welding robot and an apparatus for controlling the same,xe2x80x9d one of the inventors of which is the present inventor, discloses a method for detecting an initial welding point and a terminating welding point by means of a touch sensor tracking, after roughly setting up the type of a contact shape formed between workpieces and the initial welding point and the terminating welding point. Another Korean Patent Laid-Open No. 98-83281 titled xe2x80x9cA method for detecting an initial welding point of a welding robot,xe2x80x9d whose inventor is also the present inventor, discloses a method for detecting an exact initial welding point by means of a touch sensor tracking.
The touch sensor tracking is a method of directly detecting a position of a workpiece by means of generating an interrupt from a controller when a welding wire supplied to one end of a welding torch which is positive(+) contacts the workpiece which is negative(xe2x88x92). However, the touch sensor tracking requires a separate tracking mechanism for tracking a welding path to perform the welding operation along the welding path from the initial welding point even though the initial and terminating welding points are detected by the touch sensor tracking. That is, additional equipment such as laser vision sensor, etc. is required, for which the touch sensor tracking has not solved the problems in relation to cost and welding space.
The present invention has been made keeping in mind the above-described need, and an object of the present invention is to provide a method for correcting teaching points for a welding robot, by means of a touch sensor tracking, and a welding robot system employing the same, so that a welding path is correctly tracked, without additional sensor equipment. According to one aspect of the present invention, this and other objects may be achieved by providing a method for correcting teaching points for a welding robot having a touch sensor, comprising the steps of: mounting a workpiece to a welding jig; establishing at least one teaching point between an initial welding point and a terminating welding point; touch-sensing the workpiece at a point corresponding to the established teaching point through the touch sensor; identifying a point detected by the touch-sensing; and obtaining a new teaching point based on the difference between the established teaching point and the detection point.
Preferably, the step of obtaining the new teaching point includes the sub-steps of generating a transformation matrix based on the difference between the established teaching point and the detection point; and calculating the new teaching point by multiplying the established teaching point by the transformation matrix.
Also, the touch sensor is preferably comprised of a welding wire, provided at an end part of a welding torch.
According to another aspect of the present invention, this and another objects may also be achieved by a provision of a welding robot system comprising a welding jig supporting a workpiece, a welding robot performing a welding operation to the workpiece and having a touch sensor, and a controller for controlling the welding robot, the controller identifying a point detected by touch-sensing the workpiece mounted to the welding jig through the touch sensor between an initial welding point and a terminating welding point, obtaining a new teaching point based on a difference between a preset teaching point and the detection point, and controlling the welding robot based on the new teaching point.
Preferably, the controller generates a transformation matrix based on the difference between the preset teaching point and the detection point, and calculates the new teaching point by multiplying the preset teaching point by the transformation matrix.
Also, the touch sensor is preferably comprised a welding wire, provided at an end part of the welding torch.